Techniques of machine tools such as grinder are known in industries. For instance, R.O.C. patent Nos. M261316 and M288839 respectively disclose a machine tool that mainly include a body, a motor located in the body and a tool spindle driven by the motor to rotate. The tool spindle is coupled with two balance weights to rotate eccentrically. The two balance weights also are coupled with an action member. When the motor is started, the tool spindle is driven to rotate eccentrically. Through the two balance weights, the action member is driven to perform fabrication processes on a workpiece. However, the motor easily generates and accumulates heat during operation of the machine tool, and becomes overheated that could affect operation duration of the machine tool. As a result, durability of the machine tool also is impacted.
To remedy the aforesaid problem improving techniques have been proposed. For instance, China patent No. CN2887526 discloses a technique by forming an air inlet and an air outlet at corresponding locations of the body of a machine tool. When the motor is operating the air inlet sucks in external air and internal heat is discharged through the air outlet to cool the motor so that the problem of heat accumulation of the motor can be overcome. However, the two balance weights and action member also generate a great amount of heat during operation. The prior art CN2887526 can merely disperse heat for the motor without cooling the two balance weights. Moreover, during operation dusts are easily carried by the dispersed air to enter the motor. Hence durability of the machine tool still is a big concern.
Another improvement is disclosed in China patent No. CN201611818 in which a circular grinder has an air inlet formed at a location corresponding to a balance weight. The balance weight has an air fan to suck air through the air inlet and transmit the air downwards, and the air is then discharged via a gap between the circular grinder and a grinding disk. Such a design not only can disperse heat, also can prevent dusts from entering the motor.
However, not all machine tools respectively have a gap at the lower side to serve as an outlet of hot air. For instance, an orbital sander can suck external cooling air, but still cannot discharge internal hot air outside. Thus cooling effect is not desirable.